U.S. Pat. No. 4,304,744 (assigned to W. R. Grace) is directed to a closure assembly using a polypropylene closure cap. The patent discloses a method of lining the polypropylene closure with a polyvinyl chloride plastisol compound that is fused by microwave techniques. The patent discloses the use of phthalate plasticizers such as diisooctyl phthalate (Example 1) or butyl benzyl phthalate (col. 10, line 47). The main thrust of the patent is the microwave fusing of the lining which requires a preheating step for a good fused lining. The preheat temperature must be at least about 103.degree. C. up to about 160.degree. C. The closure assembly is made without damage to the polypropylene closure.
In U.S. Pat. No. 3,462,331 to Simons, a liner is prepared for a metal cap. A plastisol is applied to the metal cap with conductive heating and pressure. The plastisol cannot be applied to a plastic cap in the same fashion, the conductively heated plunger being releasable by the inner coating of the metal cap. With a plastic cap the liner would stick to the plunger and be released with it. The Simons patent has no suggestion of the curable vinyl chloride epoxidized oil plastisol.
It is desirable to have a curable plastisol composition that can be easily used for a lining and effectively fused, without preheating, at a temperature below 130.degree. C., say about 290.degree. F. up to about 300.degree. F., and without the need for microwave energy and without conduction heating and pressure. It is desired that the composition can be quickly and easily cured at a low temperature, say, room temperature. The curable plastisol composition should also be stable with a shelf life of at least about four to six months.